The invention relates to a security system that will enable authenticated access of an individual to a protected area by means of a remote control unit, carried by the individual, containing a transponder that on reception of an interrogation signal transmits an identification code group, and a control unit, located within the protected area which, when activated by the individual, transmits the interrogation signal and then checks the identification code group sent by the transponder and allows access for the individual to the protected area only after positive verification of the authorisation to access.
It is becoming more and more usual that an individual should want to obtain access to a protected area, such as to a vehicle protected by a locked door or to a locked garage, by means of a remote control. For the purpose of the following explanation it is assumed that the protected area implies a vehicle, but the explanation should also be taken as generally valid for any protected area to which access should only be made available to an authorised individual.
The remote control used to provide access is, in the case of a vehicle representing the protected area, preferably integrated in the actual vehicle key and will be activated by pressing a button at the vehicle. The activated remote control then transmits a signal containing an identification code group unambiguously allocated to the vehicle key. This signal is received and decoded by a receiver in the vehicle and, provided that the code group contained in the signal coincides with a corresponding code group in a control unit connected to the receiver, the vehicle door locks are released, so that the vehicle will be open and access to the interior of the vehicle will become possible.
Depending on the transmitter power available, the vehicle may be opened from a greater or lesser distance of the vehicle by means of the remote control. The energy required will be provided by a battery which is housed within the vehicle key. A great problem with this mode of enabling authenticated access to the vehicle consists in that it will no longer be possible to open the vehicle by remote control when the battery in the vehicle key can no longer supply sufficient energy to power the remote control. The individual operating the key will then be forced to resort to other measures to open the vehicle, for example by unlocking the vehicle mechanically by means of a key in the conventional way. This, however, has the great disadvantage that, when this possibility is provided, the security aspect is lost, which means that even unauthorised individuals will be able to open the vehicle by simply unlocking it with a key.
A further development of enabling authenticated access to a vehicle is a so-called passive unlocking system, where the individual is no longer actively required to activate the remote control signal. With this passive unlocking system it is sufficient for the individual to be at a relatively short distance from the vehicle, whereby the interchange of transmitted signals between the remote control unit, carried by the individual, and the vehicle to be unlocked is initiated, for example, by the individual touching the door handle as if to open the door manually. The xe2x80x9cremote controlxe2x80x9d, carried by the individual may be housed, for example, within the vehicle key or even in a so-called chip-card. In such a case, the opening procedure starts with the individual touching the vehicle door handle, whereupon a control unit within the vehicle transmits an interrogation signal which, on reception, initiates in the remote control unit the re-transmission of the identification code group used for authentication. After checking that this code group coincides with the code group stored in the vehicle, unlocking of the door locks takes place and the vehicle may be opened by the corresponding activation of an electrical unlocking mechanism. Since, in the case described, there is a relatively great distance between the vehicle and the remote control unit, for example one meter, the remote control unit must contain its own power supply in the form of a battery. This again gives rise to the unfavourable situation that authenticated access to the vehicle can no longer be guaranteed when the battery is low or inactive.
The invention, therefore, rests on the requirement to modify a security system of the type described above in such a way that, at an optimised low current consumption, the authenticated access of an individual to a protected area is made possible, even when the power supply of the remote control unit has gone low or is inactive.
According to the invention, this requirement is met in that the transponder contained in the remote control unit is a passive transponder which obtains its supply voltage from the interrogation signal sent out by the control unit and applies it to a supply voltage rail, that the remote control unit contains a battery that can be connected to the supply voltage rail by means of a controllable battery coupling switch via a high-resistance path when the remote control unit is in its quiescent state, or via a low-resistance path when the remote control unit is in its active state, that a pulse detector is provided which receives its supply voltage in the quiescent state of the remote control unit via the high-resistance path of the battery coupling switch and which, on reception of the interrogation signal by the transponder, outputs a recognition signal, that a remote-field detector is provided which receives the recognition signal and outputs a remote-field signal as soon as the value of the recognition signal comes within a pre-determined range, that a logic circuit is provided which, on reception of the remote-field signal, outputs a switching signal to the battery coupling switch which switches this into the state where the battery is connected to the supply voltage rail via the low-resistance path, and outputs an activation signal to the transponder which will cause its transmitting unit to transmit the identification code group, and that a near-field detector is provided which, on recognising a value of the supply voltage produced by the transponder exceeding a pre-determined threshold value, outputs a near-field signal that causes the logic circuit to put the battery coupling switch into the state prevailing in the quiescent state of the remote control unit, and to transmit the activation signal to the transponder.
The transponder used in the security system according to the invention can, without the need of an energy supply from a storage battery, receive and decode a signal sent by the control unit in the protected area. This may be a transponder of the type known from EP 0 301 127 B1. But to achieve a wider range of the remote control unit, a supply battery has been provided which, however, in the quiescent state of the remote control unit only delivers as much current to the circuits contained in the remote control unit as to enable it to recognise an interrogation signal sent by the control unit in the protected area, so that, as a result of this recognition process, the remainder of the circuit is brought into an active mode. The result of this activation process is that the supply battery can supply a higher current to the circuits contained in the remote control unit and consequently to enable the interrogation signal to be decoded and to transmit the identification code group at a higher transmission power. Should the individual with the remote control unit be in such close proximity to the control unit of the protected area that the near-field detector detects a high signal level and transmits the near-field signal, the battery is, once again, left almost entirely disconnected from the circuit, so that a saving in current consumption is obtained, enabling the transponder to receive and to decode the interrogation signal without making demands on the battery. The transponder can also transmit the identification code group without the supply battery having to deliver any power. The same applies when the supply battery is completely inactive, whereby in this case access authentication can be achieved when the remote control unit is moved into a very close position to the control unit of the protected area, to enable the transponder to obtain its supply voltage from the interrogation signal and the identification code group to be sent at low transmission power.
The protected area is preferentially a vehicle whose door will only be unlocked by the control unit housed in this vehicle when the identification code group sent back by the transponder corresponds to the code group expected by the control unit. In an advantageous embodiment, the control unit housed in the vehicle transmits the interrogation signal when the individual either touches or actuates the door handle of the vehicle.
It is advantageous to incorporate an aerial, forming part of the vehicle control unit, in the wing mirror on the driver""s side.